Under the assumption that is a zombie was a ninja, the zombie actually had to have higher brain functions and intelligence than the normal zombie, Adah simply wrote out that proof where 1=2 (http://www.math.toronto.edu/mathnet/falseProofs/second1eq2.html), in hopes that it would just blow its oddly functioning mind with its impracticality, and, therefor, rendering him useless. Because everyone knew the way to kill a zombie was by removing the head or, in this case, destroying the brain.